Conventionally, systems that use channel hopping protocols, including the Bluetooth/Bluetooth Low Energy (BT/BLE) protocols, involve devices (e.g., a Master and one or more Slaves) executing a same channel hopping sequence. This enables the devices to know which base frequency will be used in a given time period (i.e., window) to transmit and receive data. Channel hopping protocols can contribute to security and signal robustness.
Among numerous applications that can be provided by a system is direction finding. Some direction finding methods can rely a sinusoidal signal (a “constant tone”) transmitted from the device to be found (i.e., located device), which can be received and processed by another device (i.e., locating device) to determine the direction of the located device with respect to the locating device. Some existing protocols demand custom hardware to accommodate location finding functions. Such custom hardware can enable a located device to generate a sinusoidal signal in response to output data (e.g., an outgoing packet) or an output command.
FIG. 13 shows a conventional constant tone extension (CTE) packet that can enable the generation of a sinusoidal signal. However, the CTE packet can work only if hardware on the corresponding device can support the function. The packet includes conventional BLE packet fields, including a preamble, access address, protocol data unit (PDU), and error correction code (CRC). However, in addition it can include a constant tone extension (CTE) portion. The packet can indicate to transmitting hardware (e.g., via a particular bit setting) that it is a CTE packet. The CTE portion can be used to transmit the desired sinusoidal signal.
The above use of a CTE packet can generate the necessary signals for a direction finding application. However, as noted, the processing of a CTE packet can require custom hardware that may not be present in some devices.